An object of the present invention is to provide apparatus for detecting the breakage of a glass sheet wherein a piezoelectric transducer is secured to the surface of the glass sheet to detect mechanical vibrations or elastic waves which are generated when the glass is broken. The invention has particular application as a burglar alarm.
Another object of the invention is to provide apparatus for detecting the breakage of a glass sheet to which a piezoelectric transducer is secured and electrically excited by an impulse to introduce an elastic wave into the glass sheet, whereby the wave is reflected back to the transducer as it encounters discontinuities in the glass sheet and translated into an electrical signal for utilization as an alarm signal.